VTTCue.use = function (plugin: Function | Object) {
  //...
  const args = toArray(arguments, 1)
  args.unshift(this)
  if (typeof plugin.install === 'function') {
    // install的上下文是自己
    plugin.install.apply(plugin, args)
  } else if (typeof plugin === 'function') {
    plugin.apply(null, args)
  }
  installedPlugins.push(plugin)
  return this
}
